1. Technical Field
Embodiments of the present disclosure relate to an intermediate transfer medium conveying device suitable for conveying a belt-like intermediate transfer medium, which is wound between a winding reel and a feeding reel, by the drive force of one DC motor in a normal feed direction where the intermediate transfer medium is wound on the winding reel and in a reverse feed direction where the intermediate transfer medium is wound on the feeding reel; and a thermal transfer line printer using the intermediate transfer medium conveying device.
2. Related Art
An intermediate transfer type thermal transfer line printer, which forms a primary image by transferring ink of a multi-color ink film to an intermediate transfer medium by a line thermal head and forms an image on a medium to be transferred by re-transferring the primary image to the medium to be transferred by re-transfer means, can easily form an image on various media to be transferred, such as a CD, a CD-R, a MO, a DVD, and various types of card, in addition to plain paper and has high print quality, and qualities of low noise generation, low cost, easiness in maintenance, and the like. For this reason, the intermediate transfer type thermal transfer line printer has been widely used as an output device of a computer, a word processor, or the like in the past (for example, see Japanese Unexamined Patent Application Publication No. 2002-337373).
In a primary image forming unit, the above-mentioned thermal transfer line printer in the related art makes a line thermal head be in a head-down state where the line thermal head comes into contact with a platen roller with an ink film and an intermediate transfer medium interposed therebetween in this order and makes heat generating elements of the line thermal head selectively generate heat in this state on the basis of printing information (image forming information) while conveying the ink film and the intermediate transfer medium. As a result, ink carried on the ink film is partially melted or sublimated. Then, the thermal transfer line printer forms an inverted image as a primary image, which corresponds to one screen (one page), on the intermediate transfer medium by transferring the ink to the intermediate transfer medium. After that, the thermal transfer line printer conveys the primary image, which is formed on the intermediate transfer medium, to a portion right ahead of a re-transfer unit by conveying the intermediate transfer medium. Subsequently, after the thermal transfer line printer aligns the position of the primary image with the position of the medium to be transferred, the primary image formed on the intermediate transfer medium is melted or sublimated in the re-transfer unit by heat and pressure of re-transfer means, which is formed of a heating roller and the like. Then, the thermal transfer line printer forms (prints) a desired image on the medium to be transferred by transferring (re-transferring) and fixing the primary image to the medium to be transferred.
In this case, when a one-colored image is to be formed on the medium to be transferred, the image can be formed by one pass.
In contrast, when a multi-colored image is to be formed on the medium to be transferred, a multi-color ink film, on which ink areas corresponding to a plurality of colors are repeatedly disposed so that different colors are adjacent to each other in a longitudinal direction, is used as an ink film. After an inverted image formed by an initial color ink carried on the multi-color ink film is formed on the intermediate transfer medium, the line thermal head is in a head-up state where the line thermal head is separated from the platen roller. In this state, the intermediate transfer medium is conveyed in the reverse direction (rewound). Then, after the heading for returning the inverted image formed by the initial color ink to a transfer position is performed, a multicolored primary image is formed by a so-called swing back method of transferring an inverted image corresponding to the next color so that the inverted image corresponding to the next color is superimposed on the inverted image corresponding to the initial color.
Specifically, when a full color image is to be formed, a full color image is formed by using a multi-color ink film on which four color ink areas formed by four color inks, for example, K (black), Y (yellow), M (magenta), and C (cyan) inks are repeatedly disposed in this order so that different colors are adjacent to each other in a longitudinal direction.
That is, at first, a K-colored inverted image corresponding to one screen is formed on the intermediate transfer medium by using a K-colored (black) ink area of the multi-color ink film. Then, the heading of the K-colored inverted image, which is formed on the intermediate transfer medium, is performed by conveying the intermediate transfer medium, which has been conveyed by a primary image forming operation, in the reverse direction. Further, a Y-colored inverted image corresponding to one screen is formed so as to be superimposed on the K-colored inverted image, which corresponds to one screen and is formed on the intermediate transfer medium, by performing the heading of a Y-colored (yellow) ink area adjacent to the K-colored ink area of the multi-color ink film and using the Y-colored ink area of the multi-color ink film. Similarly hereinafter, a full color primary image corresponding to one screen is formed on the intermediate transfer medium by superimposing inverted images on the intermediate transfer medium in the order of an M-colored (magenta) ink area and a C-colored (cyan) ink area.
Here, the intermediate transfer medium is formed in the shape of a belt, and is wound between a pair of reels that is formed of a winding reel and a feeding reel. Further, the intermediate transfer medium can be conveyed in a normal feed direction (front feed) where the intermediate transfer medium is wound on a winding reel by an intermediate transfer medium conveying device and in a reverse feed direction (back feed) where the intermediate transfer medium is wound on a feeding reel.
The intermediate transfer medium conveying device includes a pair of drive shafts. The pair of drive shafts is formed of a winding shaft that rotationally drives the winding reel during normal feed where the intermediate transfer medium is conveyed in the normal feed direction, and a feeding shaft that rotationally drives the feeding reel during reverse feed where the intermediate transfer medium is conveyed in the reverse feed direction. Further, the drive shafts are directly driven by the drive force of the DC motor, so that the winding force for winding the intermediate transfer medium is controlled at an appropriate value. Furthermore, back tension is applied to each of the drive shafts by a torque limiter, which is disposed between the drive shaft and the reel, during the normal feed where the intermediate transfer medium is conveyed in the normal feed direction and during the reverse feed where the intermediate transfer medium is conveyed in the reverse feed direction. For example, a torque limiter, which includes an inner cylinder as an inner ring, an outer cylinder as an outer ring, and a spring (coil spring) interposed between the inner and outer cylinders, is used as the torque limiter from the past (for example, see Japanese Unexamined Patent Application Publication No. 2002-147499).
Intermediate transfer medium conveying devices, which apply back tension by the torque limiter in the related art, have had a problem in that the intermediate transfer medium cannot be appropriately conveyed. That is, when the conveying direction of a transfer medium is inverted, a winding operation is performed in a state where back tension is not applied to the feeding side by the “play (backlash)” of the torque limiter. Accordingly, slack is generated on the intermediate transfer medium.
The “play” of the torque limiter may be play (backlash) between tooth surfaces when a pair of gears mesh with each other.
Further, the “play” of the torque limiter is in the range of 10 to 20° in the circumferential direction about the center of the torque limiter, and is generated when the conveying direction of the intermediate transfer medium is inverted to the reverse feed direction from the normal feed direction and when the conveying direction of the intermediate transfer medium is inverted to the normal feed direction from the reverse feed direction.
Moreover, a slack removing mechanism for removing the slack of an intermediate transfer medium, which is caused by the “play” of the torque limiter, is disposed in the intermediate transfer medium conveying device in the related art in order to appropriately convey the intermediate transfer medium. The slack removing mechanism is formed of tension applying shafts, such as tension bars or tension rollers, which are disposed on the conveying path of the intermediate transfer medium, specifically, on at least one of both sides of a primary image forming unit, preferably, on both sides of the primary image forming unit (for example, see Japanese Unexamined Patent Application Publication No. 2002-337410).
Further, as the intermediate transfer medium conveying device, there is proposed an intermediate transfer medium conveying device including torque limiters (spring type torque limiters) that transmit the drive force of a DC motor to both the drive shafts through a worm gear (crossed helical gear) and are disposed between a driving gear train connected to the worm gear and the drive shafts, respectively, in order to prevent the slack of the intermediate transfer medium that is caused by the “play” of a torque limiter (for example, see Japanese Unexamined Patent Application Publication No. 2007-112007).
However, the thermal transfer line printer using the intermediate transfer medium conveying device in the related art requires a slack removing mechanism for removing the slack of the intermediate transfer medium. For this reason, the structure of the printer is complicated. Accordingly, there has been a problem in that costs are large.
Furthermore, in the thermal transfer line printer using the intermediate transfer medium conveying device in the related art, the parallelism of the tension applying shafts of the slack removing mechanism, that is, the deviation between the width direction orthogonal to the conveying direction of the intermediate transfer medium and the axial direction of the shaft affects the deviation of the conveying position of the intermediate transfer medium. For this reason, an adjusting mechanism for adjusting parallelism is required. Accordingly, the structure of the printer is complicated. Therefore, there has been a problem in that costs are large.
Further, in the thermal transfer line printer using the intermediate transfer medium conveying device including a worm gear in the related art, the slack of the intermediate transfer medium, which is caused by the “play” of the torque limiter connected to the winding shaft, is hardly generated when the conveying direction of the intermediate transfer medium is inverted. However, since the winding force for winding the intermediate transfer medium is determined by the set value of the torque of the torque limiter, there has been a problem in that it may not be possible to change a winding force of the winding shaft for winding the intermediate transfer medium during the normal feed even though a voltage applied to the DC motor (the rotational speed of the DC motor) is changed. That is, since it may not be possible to change a winding force of the winding shaft for winding the intermediate transfer medium during the normal feed, there has been a problem in that it may also not be possible to appropriately convey the intermediate transfer medium.
As a result, in the thermal transfer line printer using the intermediate transfer medium conveying device including the worm gear in the related art, there has been a problem in that it may not be possible to optimize each of the winding force for winding the intermediate transfer medium during the transfer where a primary image is formed on the intermediate transfer medium and the winding force for winding the intermediate transfer medium during the re-transfer where the primary image is re-transferred to a medium to be transferred.
Meanwhile, an optimum winding force for winding the intermediate transfer medium, which is required to separate ink from the ink film and transfer the ink to the intermediate transfer medium during the transfer, is smaller than an optimum winding force for winding the intermediate transfer medium, which is required to separate the primary image from the intermediate transfer medium and transfer the primary image to the medium to be transferred during the re-transfer.
Further, there is demand for an intermediate transfer medium conveying device that can appropriately convey an intermediate transfer medium, and a thermal transfer line printer using the intermediate transfer medium conveying device.
These and other drawbacks exist.